Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during the periovulatory phase of the oestrous cycle in the cow

Abstract

An injection of 500 micrograms prostaglandin (PG) analogue was given on Day 12 (mid-luteal phase) of the oestrous cycle to 8 cows. An LH surge occurred 59 +/- 2 h later. LH, FSH, prolactin, oestradiol-17 beta, progesterone and oxytocin concentrations were determined in blood samples collected from the caudal vena cava and/or the jugular vein at 20-min (5 cows) or 5-min (3 cows; only LH and FSH concentrations were determined) intervals for 24 h, beginning 48 h after the PG injection. Oxytocin concentrations were low and similar in the vena cava and the jugular vein. In blood samples collected every 5 min the interpulse interval for LH and FSH during the period before the LH surge was 38-40 min. In the 20-min samples the interpulse interval for oestradiol was similar to that for LH and FSH, but pulse amplitude and basal concentrations steadily increased to reach maximum concentrations 6-8 h before and again during the LH surge. A decrease in oestradiol concentrations, lasting at least 60 min, occurred just before the start of the LH surge. Progesterone concentrations also increased at the same time as the LH surge. The magnitude of the LH surges varied from 7 to 32 ng/ml, but all cows ovulated and had oestrous cycles of normal length. Distinct pulses of LH and FSH were observed throughout the LH and FSH surges. Pulsatile secretion of LH was not detected for a period of up to 6-12 h following the LH surge, but then low-amplitude pulses occurred. In contrast, the pulsatile secretion of FSH remained at a frequency similar to that observed during the descending phase of the FSH surge. Furthermore, a second increase in FSH concentrations occurred, beginning 4-12 h after the LH-surge. It is concluded that: (1) the frequent, high-amplitude pulses of oestradiol that occur before and during the LH surge are probably due to stimulation by pulses of LH; (2) the LH surge is the result of an increase in frequency and amplitude of the LH pulses; (3) the second increase in FSH that follows the LH and FSH surges appears to be the result of an increase in the amplitude (not frequency) of the FSH pulses; and (4) very little, if any, oxytocin is secreted from the ovary during the periovulatory phase of the oestrous cycle.

Progesterone, oestradiol-17 and LH during the oestrous cycle of muskoxen (Ovibos moschatus)

“…This period is apparently longer and more variable than in the ewe (Baird & Scaramuzzi, 1976;Karsch et ai, 1979), goat (Mori & Kano, 1984) and cow (Walters & Schallenberger, 1984). The duration of the LH surge (24 h) was longer than the 6-10 h reported for cattle (Walters & Schallenberger, 1984), 7-8 h for goats (Mori & Kano, 1984) or 14 h for the ewe (Pant et ai, 1977). In roe deer the LH peak occurred over a period of days (Schams et ai, 1980).…”

Local Release of Progesterone and Oxytocin from Microdialyzed Corpus Luteum in Superovulated Ewes: Characterization during the Non-breeding Season.

“…OT is released into the circulation in a pulsatile manner during the estrous cycle in ewes [4] and cows [5,6]. During luteal regression even when the basal OT secretion is already quite low, a pulsatile release of OT from the CL is observed correlating with prostaglandin F 2α(PGF2α) from the uterus [7].…”

Pulsatile LH secretion during the preovulatory surge in the ewe : experimental observations and theoretical considerations

“…Detailed examination of the preovulatory LH profiles of women, cows rats and monkeys has revealed that the surge is also composed of pulses rather than a massive continuous release of hormone (Midgley and Jaffe, 1971 ;Rahe et al, 1980 ;Gallo, 1981 ;Marut et al, 1981 ;Walters and Schallenberger, 1984). The pulses are very frequent and of high amplitude compared to those secreted tonically, and it has been proposed that the changes in LH concentration that describe the surge can be entirely explained by changes in pulse frequency and amplitude (Gallo, 19811.…”